Understanding users and how they use medical devices is important if you want to involve usability or human factors engineering as a prediction tool for how they may be used in real life. Researching and evaluating users in theory and practice with medical devices should give confidence in the potential uptake and use, which it would be hoped, would be safe, effective and efficient. But one area that can be very predictive is the understanding of the mental models users have and follow, purely since these are unlikely to change significantly over time, or at least until another product alters a mental model.

People use products in a similar manner – we all follow our own mental models when using products. These mental models are based upon prior experience, product history, training, learning and logic. With all of these mental models, if they can be generalised and trended, then they can, to an extent, become predictable. An example will be how we all carry a mug of hot coffee – using the handle or carrying it using the base. Both of these mental models can be predicted, and this means that the use-based risks can be calculated to be much more accurate, knowing which mental models will be applied to the task.

If we determine that 60% of people who will carry a volume of hot coffee in a mug by its handle, and 20% by holding the base of the mug, then we have 80% who will carry the mug in two ways. This can be extremely useful when assessing concept designs, developing devices towards the final design, and especially when attempting to predict how safe to use a device is in human factors and usability testing. After all no one wants to spend time testing a device that is potentially unsafe and unusable!

Understanding mental models is key to ensuring the design is suited to the intended users of a product. If the mental model of an existing task, method or action is changed by the device, then you are altering the mental model the user needs to have. Small and incremental changes may enhance and improve the safety profile, but a large or step change in the mental model could have the opposite effect. Usability is a performance indicator, and based upon elements such as learnability, efficiency and ease of use. If a product is to change or alter a mental model, then understanding how much the change is could be valuable, but also knowing how people may learn the product, use it and deal with the change in mental model may enable a high level of prediction.

Learning

Users of medical devices in hospitals have time to learn how to operate medical devices. They are trained on their safe use and are assessed on their actual use of the device. As such, any mental models they may have will be based upon specific clinical practices and experience of using other, similar medical devices. Where there are differences in clinical practices, there may be differences in the users mental models, and this may lead to adverse incidences arising. Users may resort to using previous mental models, especially when under pressure or time constraints – frequently observed in hospital locations.

It is different in the home environment though. Here, learning can be a variable option. Some devices require structured training, and some devices, such as “over-the-counter” devices may rely solely on self-learning. New users may not have a preconceived mental model which is an ideal situation, since their first experience or training will create that mental model. Existing users may a very “set-in-stone” mental model that they have to change. Some existing users will embrace a change in their mental models if they either are having a negative user experience with their current devices, or can see the benefits of the replacement device. Some may not like it initially, at first.

Changing mental models

It is not always easy to change a users’ mental model. It is even more difficult to change thousands of users mental models. If users have to change from one device to another – for cost, security, availability or safety reasons, then it is prudent to assess and compare the mental models users may have. The key here is to understand the potential gaps or differences – the changes, and also the effect of the changes. An example would be if a user is used to delivering their medication using a pen injector that has the injection button on the non-needle end. If they are used to pressing this button to deliver the injection, and it works well for them, then this has created a strong mental model. If then, the pen injector has to be switched for another model to deliver the same medicine, and on this particular pen injector the injection button is on the side, and not at the non-needle end, then there is a requirement to alter the users existing mental model of the injection.

The change may be managed very simply with training and suitable instructions, and of course a very easy-to-press and obvious injection button. The impact of the change may appear small – you are not removing the injection button, just moving it on the device. But what you are doing is to completely change how the user will have to hold and grip the pen injector. If the user is the recipient (patient user), then this may cause more ergonomic and use-based risk. If the user is not the recipient, but the deliverer (healthcare professional, carer), then this may cause less ergonomic use-based risk. The upshot, is that it is valuable to not just assess the change, but the impact of the change on the user – and it depends on the user, their role, the use environment and many more human factors.

Conclusion

Users are unpredictable and variable. But most have commonality in that we share many of the same mental models. By having similar mental models, then the usability of the device can to an extent be predicted – at least in theory. When usability testing and human factors evaluations take place, then these mental models can be observed and quantified. By developing devices using a human factors or usability engineering process (IEC62366-1/2, FDA or MHRA guidance as examples), then during the user research phase of the development, the mental models can be determined and assessed. Whilst the design of the device develops, these mental models can continue to be assessed against the design to the point it is final. During formative tests, the mental models can be evaluated with the developing design, and in essence, verified. During summative testing though, the mental models are validated – and they need to meet the users needs.

Minimising the change to users mental models will be the aim with any medical device development, but where there are potential changes to these mental models, it is valuable to define and test them out, so that even if there are significant changes, they pose no added safety risk. Of course, the ultimate is that a mental model aids the use of a device, making it safer to use and a positive user experience.

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